What is this bag lacking that makes it not "even close to a substitute?"

True insulated bottle holders (2 of them), solid stability without having to build your own PVC frame, designated mini pocket, pencil pockets, rainfly, rails on the bottom, choosing between tucking in the front flap and losing the pockets for storage or always having to open the front flap to get discs.

Don't get me wrong, I'm a big fan of the DIY bag. I have two in my sig. But he's right, they're not true substitutes for bags built for disc golf. They're cheaper and they hold discs. If that's what you're after, then spend less and enjoy. Nothing wrong with it.